ESP applications are typically defined as high-speed if the pump shaft is spinning at a rate over 4500 RPM.
The average formation solids concentration in production flow from Russian wells is about 0.2 g/liter. In case of heavy oil production this parameter can be much higher. The concentration of proppant flowback in production flow can reach concentrations as high as 1 g/liter immediately after fracturing. A high rotational speed combined with high solids concentration in the production flow causes accelerated erosion wear of pump stages. Solids can be trapped inside small gaps between spinning and stationary components of a pump stage to produce abrasion in the stage material. As a result, the pump efficiency decreases. Stage wear also leads to an increase in dynamic loads for journal bearings. Accelerated wear of radial bearings may be a cause for premature pump failure. The theory of erosion teaches that erosive wear rate is proportional to the square of the velocity of the particles. For example, the pump rate growth from 3500 RPM to 7000 RPM will result in 4-times growth in the erosion wear rate of the stage. With current oil industry trends to increase production rates by operating of pumps at higher RPM, the erosion-protective elements became a vital feature for pump design.
RU 2,018,716 discloses a multistage centrifugal pump comprising a housing, guide vanes, shaft with impeller, intermediate spacers. A protective coating of wear-resistant material deposited, at least, in the places of shaft bending under the load exerted by intermediate bushings and guide vanes is disclosed. Protective coatings for opposite surfaces of guide vanes and spacers are made of superhard self-fluxing chrome-nickel alloy and/or superhard nickel-aluminum material.
The shortcoming of this design is a low resistance to abrasive impact by particles suspended in the fluid.
RU 2,132,000 discloses a multistage centrifugal pump comprising a housing, guiding apparatuses installed inside the housing through end and intermediate bearing supports, a shaft with an alternating arrangement of impellers and spacers. Each impeller has an annular support comprising a lower disk for delivering axial loads to the housing during pump operation. Each intermediate spacer is made from two ring U-like items telescopically mated to each other. These have holes in the base, so one U-shaped item is tightly fixed between the guiding apparatuses, and axial mobility of the other U-shaped item is provided by the size of the longitudinal groove in the immobile item and the peg matched to the groove of immobile item. The base of the item has two lugs, one is required for contact with the annular support of the impeller above, and the other lug is required for closure of the ring-like cavity created by the external cylindrical surface of the protective bushing and the inside wall of the immobile U-shaped item, and external side of the mobile U-shaped item. This ring-like cavity accommodates an elastic material, e.g., fluoroplastic or its composites.
The shortcoming of this pump is complex design and low stability to impact of abrasive particles suspended in the pumped fluid.
SU 1,763,719 discloses a multistage submersible centrifugal pump. This pump consists of a cylindrical housing with many stages. Each stage is installed on the shaft with axial freedom for the impeller (with hub) and the diffuser, that includes a vaned disk fixed to the housing with a central orifice and vanes on the end facing the impeller, and an external disk with a hub. At this point, the surfaces of the orifice of the vaned disk and the hub of the external disk produce an annular channel. At least part of diffusers are equipped with intermediary spacers forming the inside surfaces of the hubs. The diffusers with intermediary spacers are equipped with damping O-rings; they are equipped with windows and made from an elastic material; the rings are laid into the inlet annular channels.
The drawback of this pump is low resistance to abrasive particles suspended in the pumped fluid.
The object of this invention is to provide a new design of submersible pump which can potentially give a longer service life than the prior art designs.